Studies on the secondary structure of intraphage T-7 DNA.

Secondary structure of intraphage DNA of coliphage T-7 was studied by spectrophotometry and electron microscopy. T-7 DNA in vivo showed 7% hyperchromicity, on the average, compared to DNA released by heating the phage 30 min at 55 - 60 °C. The intraphage DNA when melted by heating the phage for 13 min at 95° and then rapidly chilled, was found to be defficient in hyperchromic rise by about 10% compared to isolated T-7-DNA treated under similar conditions. Electron micrographs of T-7-DNA released by osmotic shock revealed that the incompletely released molecules showing a pattern possessed denatured regions in the form of single-stranded loops. Phenol extracted T-7-DNA molecules as well as T-7 genomes completely released by osmotic shock did not show any pattern and possessed no denatured zones. These results helped to infer that intraphage T-7-DNA is partially denatured.